JP4666007B2 - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
- Publication number
- JP4666007B2 JP4666007B2 JP2008143511A JP2008143511A JP4666007B2 JP 4666007 B2 JP4666007 B2 JP 4666007B2 JP 2008143511 A JP2008143511 A JP 2008143511A JP 2008143511 A JP2008143511 A JP 2008143511A JP 4666007 B2 JP4666007 B2 JP 4666007B2
- Authority
- JP
- Japan
- Prior art keywords
- catalyst
- iron oxide
- oxide particles
- particles
- nox
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 239000003054 catalyst Substances 0.000 title claims description 178
- 238000000746 purification Methods 0.000 title claims description 33
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 296
- 239000002245 particle Substances 0.000 claims description 206
- 239000000463 material Substances 0.000 claims description 74
- 239000007789 gas Substances 0.000 claims description 57
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 43
- 239000001301 oxygen Substances 0.000 claims description 43
- 229910052760 oxygen Inorganic materials 0.000 claims description 43
- 239000011230 binding agent Substances 0.000 claims description 31
- 238000003860 storage Methods 0.000 claims description 23
- 229910052751 metal Inorganic materials 0.000 claims description 21
- 239000002184 metal Substances 0.000 claims description 21
- 229910052595 hematite Inorganic materials 0.000 claims description 6
- 239000011019 hematite Substances 0.000 claims description 6
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 6
- 150000002739 metals Chemical class 0.000 claims description 6
- 229910052697 platinum Inorganic materials 0.000 claims description 5
- 229910052703 rhodium Inorganic materials 0.000 claims description 5
- 229910052598 goethite Inorganic materials 0.000 claims description 4
- AEIXRCIKZIZYPM-UHFFFAOYSA-M hydroxy(oxo)iron Chemical compound [O][Fe]O AEIXRCIKZIZYPM-UHFFFAOYSA-M 0.000 claims description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 4
- 239000002994 raw material Substances 0.000 claims 1
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 240
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 60
- 239000010410 layer Substances 0.000 description 38
- 239000002131 composite material Substances 0.000 description 30
- 238000001179 sorption measurement Methods 0.000 description 27
- 230000032683 aging Effects 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 21
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 19
- 239000000843 powder Substances 0.000 description 19
- 229910052717 sulfur Inorganic materials 0.000 description 19
- 239000011593 sulfur Substances 0.000 description 19
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 18
- 208000005374 Poisoning Diseases 0.000 description 17
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 17
- 238000009826 distribution Methods 0.000 description 16
- 238000013507 mapping Methods 0.000 description 16
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 16
- 231100000572 poisoning Toxicity 0.000 description 16
- 230000000607 poisoning effect Effects 0.000 description 16
- 239000002002 slurry Substances 0.000 description 15
- 238000010304 firing Methods 0.000 description 14
- 229910052742 iron Inorganic materials 0.000 description 10
- 238000001035 drying Methods 0.000 description 9
- 239000000243 solution Substances 0.000 description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 9
- 239000013078 crystal Substances 0.000 description 8
- 230000009467 reduction Effects 0.000 description 8
- 210000002421 cell wall Anatomy 0.000 description 7
- 238000005259 measurement Methods 0.000 description 7
- 229910044991 metal oxide Inorganic materials 0.000 description 7
- 150000004706 metal oxides Chemical class 0.000 description 7
- 229910000510 noble metal Inorganic materials 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000000851 scanning transmission electron micrograph Methods 0.000 description 7
- 229910052684 Cerium Inorganic materials 0.000 description 6
- 239000000446 fuel Substances 0.000 description 6
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 6
- 239000010948 rhodium Substances 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000011068 loading method Methods 0.000 description 5
- 239000011148 porous material Substances 0.000 description 5
- 229910052726 zirconium Inorganic materials 0.000 description 5
- 229910002651 NO3 Inorganic materials 0.000 description 4
- 229910021536 Zeolite Inorganic materials 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 4
- 238000002156 mixing Methods 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 229910052723 transition metal Inorganic materials 0.000 description 4
- 150000003624 transition metals Chemical class 0.000 description 4
- 239000010457 zeolite Substances 0.000 description 4
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 3
- 150000001342 alkaline earth metals Chemical class 0.000 description 3
- 239000002585 base Substances 0.000 description 3
- 238000001354 calcination Methods 0.000 description 3
- 230000003197 catalytic effect Effects 0.000 description 3
- 229910000420 cerium oxide Inorganic materials 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 3
- 238000011946 reduction process Methods 0.000 description 3
- 239000011232 storage material Substances 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- -1 Pt and Rh Chemical class 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 229910052783 alkali metal Inorganic materials 0.000 description 2
- 150000001340 alkali metals Chemical class 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 210000004027 cell Anatomy 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 229910052878 cordierite Inorganic materials 0.000 description 2
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 230000003993 interaction Effects 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 230000036962 time dependent Effects 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 239000003463 adsorbent Substances 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- IXSUHTFXKKBBJP-UHFFFAOYSA-L azanide;platinum(2+);dinitrite Chemical compound [NH2-].[NH2-].[Pt+2].[O-]N=O.[O-]N=O IXSUHTFXKKBBJP-UHFFFAOYSA-L 0.000 description 1
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical group [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000008034 disappearance Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- JEGUKCSWCFPDGT-UHFFFAOYSA-M hydroxide;hydrate Chemical compound O.[OH-] JEGUKCSWCFPDGT-UHFFFAOYSA-M 0.000 description 1
- 229910052809 inorganic oxide Inorganic materials 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000004643 material aging Methods 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 150000002910 rare earth metals Chemical class 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- RXSHXLOMRZJCLB-UHFFFAOYSA-L strontium;diacetate Chemical compound [Sr+2].CC([O-])=O.CC([O-])=O RXSHXLOMRZJCLB-UHFFFAOYSA-L 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000003878 thermal aging Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Landscapes
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Description
本発明は、排気ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purification catalyst.
軽油を主成分とする燃料を用いるディーゼルエンジンや、ガソリンを主成分とする燃料を用いて希薄燃焼させるリーンバーンガソリンエンジンのような希薄燃焼式エンジンでは、その排気ガス中にNOx(窒素酸化物)が多く含まれる。そこで、排気ガスの酸素濃度が高いときに排気ガス中のNOxを吸蔵し、その酸素濃度が低下したときに当該NOxを放出するNOxトラップ材を設け、放出するNOxを排気ガス中のHC(炭化水素)と反応させることにより還元するようにした、所謂NOx吸蔵還元型触媒が一般に知られている。 NOx (nitrogen oxide) is contained in the exhaust gas of a lean combustion engine such as a diesel engine using a fuel mainly composed of light oil or a lean burn gasoline engine that performs a lean combustion using a fuel mainly composed of gasoline. Many are included. Therefore, a NOx trap material that stores NOx in the exhaust gas when the oxygen concentration of the exhaust gas is high and releases the NOx when the oxygen concentration decreases is provided, and the released NOx is converted into HC (carbonized carbon) in the exhaust gas. So-called NOx occlusion reduction type catalysts which are reduced by reacting with (hydrogen) are generally known.
このNOx吸蔵還元型触媒は、一般には、アルミナ、酸素吸蔵放出能をもつCe含有酸化物、触媒金属としてのPtやRh、並びにNOxトラップ材としてのアルカリ金属やアルカリ土類金属を含有する。そのPtを担持したアルミナは、排気ガス中のNOをNO2に酸化することでNOxトラップ材に吸蔵され易くする。例えば、NOxトラップ材としてBaを採用した場合、Ba(NO3)2となってNOxが吸蔵される。Ce含有酸化物は、PtやRhの酸化還元状態をコントロールしてNOx浄化を促進するとともに、NOxを捕捉する働きも有する。しかし、このCe含有酸化物によるNOxの捕捉は、Ba等のNOxトラップ材とは違って、NOxの表面吸着を主体にしていると考えられ、Ce含有酸化物の比表面積はそれほど大きくないことから、NOxを多量に吸着することはできないと考えられている。 This NOx storage-reduction catalyst generally contains alumina, a Ce-containing oxide having oxygen storage / release ability, Pt and Rh as catalyst metals, and alkali metals and alkaline earth metals as NOx trap materials. Its Pt alumina carrying is easily occluded in the NOx trap material by oxidizing NO in the exhaust gas to NO 2. For example, when Ba is adopted as the NOx trap material, it becomes Ba (NO 3 ) 2 and NOx is occluded. The Ce-containing oxide controls NOx reduction of Pt and Rh to promote NOx purification and also has a function of capturing NOx. However, unlike NOx trap materials such as Ba, NOx trapping by this Ce-containing oxide is considered to be mainly due to the surface adsorption of NOx, and the specific surface area of the Ce-containing oxide is not so large. It is believed that NOx cannot be adsorbed in large amounts.
ところで、近年はPt、Rh等の希少金属の資源保護のため、触媒中へのこれら触媒金属の含有量を低減する研究が活発化している。 By the way, in recent years, in order to protect resources of rare metals such as Pt and Rh, research for reducing the content of these catalytic metals in the catalyst has been activated.
例えば特許文献1には、触媒金属量を増大させることなく、酸素吸蔵材の酸素吸蔵放出能を向上させるようにした触媒の例が記載されている。それは、セリウム酸化物を含む担体と、この担体に担持された遷移金属及び貴金属からなる触媒金属とよりなり、セリウム原子及び貴金属各々に対する遷移金属の原子比を所定の範囲にするというものである。遷移金属としては、Co、Ni及びFeの少なくとも一種が好ましいとされている。但し、実施例として開示されているのはCo及びNiだけであり、Feについての実施例はない。 For example, Patent Document 1 describes an example of a catalyst that improves the oxygen storage / release capability of an oxygen storage material without increasing the amount of catalyst metal. It consists of a support containing cerium oxide and a catalyst metal comprising a transition metal and a noble metal supported on the support, and the atomic ratio of the transition metal to each of the cerium atom and the noble metal is within a predetermined range. As the transition metal, at least one of Co, Ni and Fe is considered preferable. However, only Co and Ni are disclosed as examples, and there is no example about Fe.
また、特許文献1では、セリアジルコニア固溶体粉末に硝酸Ni(又は硝酸Co)を含浸させ、蒸発乾固、乾燥及び焼成を行ない、得られた粉末にPt溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。そして、この触媒粉末とRh/ZrO2粉末とAl2O3粉末とアルミナゾルとイオン交換水とを混合してスラリーを調製し、このスラリーをハニカム担体にウォッシュコートして触媒層を形成するとされている。 In Patent Document 1, ceria zirconia solid solution powder is impregnated with Ni nitrate (or Co nitrate), evaporated to dryness, dried and fired, and the obtained powder is impregnated with Pt solution, evaporated to dryness, dried and dried. It is said that catalyst powder is obtained by firing. The catalyst powder, Rh / ZrO 2 powder, Al 2 O 3 powder, alumina sol, and ion exchange water are mixed to prepare a slurry, and this slurry is washed on a honeycomb carrier to form a catalyst layer. Yes.
特許文献2には、CeO2−ZrO2複合酸化物よりなる担体と、該担体に担持されたAl、Ni及びFeから選ばれる少なくとも一種の金属酸化物粒子と、該担体に担持された貴金属とからなる排気ガス浄化用触媒が開示されている。担体上での貴金属の移動を金属酸化物粒子によって規制することにより、貴金属のシンタリングを抑制するというものである。但し、実施例として開示されている金属酸化物粒子はAl2O3のみであり、CeO2−ZrO2複合酸化物と硝酸Al水溶液とを混合し、これにアンモニア水を滴下・中和して沈殿を析出させ、濾過・洗浄・乾燥・焼成を行ない、得られた粉末にPt溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。Ni及びFeについての実施例はない。 Patent Document 2 discloses a support made of a CeO 2 —ZrO 2 composite oxide, at least one metal oxide particle selected from Al, Ni, and Fe supported on the support, and a noble metal supported on the support. An exhaust gas purifying catalyst is disclosed. By restricting the movement of the noble metal on the support by the metal oxide particles, sintering of the noble metal is suppressed. However, the metal oxide particles disclosed as examples are only Al 2 O 3 , CeO 2 —ZrO 2 composite oxide and Al nitrate aqueous solution are mixed, and ammonia water is dropped and neutralized thereto. It is said that a catalyst powder is obtained by precipitating a precipitate, filtering, washing, drying and calcining, impregnating the obtained powder with a Pt solution, and evaporating to dryness, drying and calcining. There are no examples for Ni and Fe.
また、特許文献3には、Fe及び/又はCeを含有するβゼオライトを含む第一触媒層(上層)と、貴金属と酸化セリウム系材料とを含む第二触媒層(下層)とを有するNOx浄化触媒が記載されている。これは、上述のNOx吸蔵還元型触媒とは異なり、排気ガスの空燃比をリーンにして、排気ガス中のNOを第一触媒層の貴金属によりNO2に酸化させて酸化セリウム系材料に吸着させ、次いで排気ガスの空燃比をリッチにすることにより、当該吸着NO2をNH3に還元させて第一触媒層のゼオライトに吸着させ、再び排気ガスの空燃比をリーンにすることにより、上記NH3と排気ガス中のNOxとを反応させてN2とH2Oとに転化するというものである。従来のゼオライトを含有するリーンNOx浄化触媒においては、Ptがゼオライトに担持ないしはイオン交換されているケースが多いが、Ptの一部をFe又はCeで置き換えることができるならば、Ptの使用量を低減することができる。
ところで、酸化鉄は、CeO2と同じく、酸素吸蔵放出能を有することが知られている。従って、特許文献1,2に記載されているCeO2−ZrO2複合酸化物のようなCe含有酸化物粒子に酸化鉄を担持させることが考えられる。そこで、本願発明者は、Ce含有酸化物粉末に硝酸鉄を含浸させて蒸発乾固、乾燥及び焼成を行ない、得られた粉末の酸素吸蔵放出能を調べた。その結果、酸素吸蔵放出能の向上が認められたものの、その向上はそれほど大きなものではなく、また、長期の使用を想定した所定の熱エージングを行なったところ、酸素吸蔵放出能がかなり低いレベルまで低下することがわかった。また、上記硝酸鉄により得られる酸化鉄粒子はその粒径が500nm以上の大きな粒子であることがわかった。 By the way, it is known that iron oxide has an oxygen storage / release capability like CeO 2 . Therefore, it is conceivable that iron oxide is supported on Ce-containing oxide particles such as CeO 2 —ZrO 2 composite oxides described in Patent Documents 1 and 2 . Therefore, the inventors of the present application impregnated Ce-containing oxide powder with iron nitrate, evaporated to dryness, dried and fired, and examined the oxygen storage / release ability of the obtained powder. As a result, although an improvement in the oxygen storage / release capability was observed, the improvement was not so great, and when the prescribed thermal aging was performed assuming long-term use, the oxygen storage / release capability was reduced to a considerably low level. It turns out that it falls. Moreover, it turned out that the iron oxide particle obtained by the said iron nitrate is a big particle | grain whose particle size is 500 nm or more.
また、本願発明者は、酸素吸蔵放出能を有するCe含有酸化物がNOx吸着能を有することから、同じく酸素吸蔵放出能を有する酸化鉄がNOxの吸着に何らかの効果を発現するのではないかという点に着眼し、Ce含有酸化物に硝酸鉄を含浸させて、NOx吸着能を評価した。その結果、硝酸鉄を含浸担持させると、NOx吸着能が幾分向上するものの、大きな向上効果は望めなかった。 In addition, the present inventor said that the Ce-containing oxide having oxygen storage / release ability has NOx adsorption ability, so that iron oxide having the same oxygen storage / release ability may have some effect on NOx adsorption. Focusing on the point, the NOx adsorption ability was evaluated by impregnating Ce-containing oxide with iron nitrate. As a result, when iron nitrate was impregnated and supported, the NOx adsorption ability was somewhat improved, but a great improvement effect could not be expected.
以上の説明から明らかなように、本発明の課題は、酸化鉄を有効に利用して触媒のNOx浄化性能を高める、特に排気ガス温度が低い低温時から高温時まで広い温度範囲にわたってNOxを効率良く浄化できるようにすることにある。 As is apparent from the above description, the object of the present invention is to effectively utilize iron oxide to improve the NOx purification performance of the catalyst. In particular, the efficiency of NOx is improved over a wide temperature range from a low exhaust gas temperature to a high temperature. There is to be able to clean well.
また、従来より、NOx浄化触媒では、NOxトラップ材の硫黄被毒による性能低下が問題になっている点に鑑み、本発明は、NOx浄化触媒の耐硫黄被毒性を改善することを課題とする。 Further, in view of the problem that the NOx purification catalyst has a problem in that the NOx trapping material is poisoned by sulfur poisoning, it is an object of the present invention to improve the sulfur poisoning resistance of the NOx purification catalyst. .
また、NOx浄化触媒では、排気ガスの空燃比がリーンからリッチ側へ変化しNOxトラップ材からNOxが放出されたときに、該NOxがNH3に還元されて排出されてしまう点に鑑み、本発明は、そのNH3の排出を抑制することも課題とする。 Further, in the NOx purification catalyst, in view of the fact that when the air-fuel ratio of the exhaust gas changes from lean to rich and NOx is released from the NOx trap material, the NOx is reduced to NH 3 and discharged. Another object of the invention is to suppress the discharge of NH 3 .
また、別の本発明の課題は、酸化鉄を、上記NOx浄化に利用するだけでなく、担体に触媒層を形成するためのバインダとしても利用することにある。 Another object of the present invention is to use iron oxide not only for the NOx purification, but also as a binder for forming a catalyst layer on the carrier.
本発明は、このような課題を解決するために、粒径の小さな微細酸化鉄粒子を触媒層に多数分散させるようにした。 In the present invention, in order to solve such problems, a large number of fine iron oxide particles having a small particle diameter are dispersed in the catalyst layer.
すなわち、本発明は、担体上に、酸素吸蔵放出能をもつCe含有酸化物粒子と、該Ce含有酸化物粒子以外のNOxトラップ材と、触媒金属としてPtとRhとを有する触媒層が形成されている排気ガス浄化用触媒であって、
上記触媒層には、酸化鉄粒子が多数分散して含まれ、少なくとも一部の酸化鉄粒子は粒径が300nm以下の微細酸化鉄粒子であり、上記Ce含有酸化物粒子及びNOxトラップ材に当該微細酸化鉄粒子が接触しており、電子顕微鏡観察において、上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が30%以上であることを特徴とする。
That is, according to the present invention, a Ce-containing oxide particle having oxygen storage / release ability, a NOx trap material other than the Ce-containing oxide particle, and a catalyst layer having Pt and Rh as catalyst metals are formed on a carrier. An exhaust gas purification catalyst,
The catalyst layer includes a large number of dispersed iron oxide particles, at least some of the iron oxide particles are fine iron oxide particles having a particle size of 300 nm or less, and the Ce-containing oxide particles and the NOx trap material The fine iron oxide particles are in contact with each other, and the area ratio of the fine iron oxide particles to the total area of the iron oxide particles is 30% or more in observation with an electron microscope.
上記粒径300nm以下の微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が30%以上であるということは、この微細酸化鉄粒子が触媒層に多数分散して含まれていることを意味する。また、上記Ce含有酸化物粒子はその二次粒子径が数μmであることが通常であるから、少なくとも一部のCe含有酸化物粒子には、複数の微細酸化鉄粒子が分散して接触しており、且つ該Ce含有酸化物粒子に対する微細酸化鉄粒子の付着量が比較的多いことを意味する。そうして、後述の実施例で明らかになるが、本発明によれば、触媒のNOx浄化性能が高くなるとともに、耐硫黄被毒性が高まり、さらに、NH3の排出が抑制される。 That the area ratio of the fine iron oxide particles having a particle size of 300 nm or less to the total area of the iron oxide particles is 30% or more means that a large number of fine iron oxide particles are dispersed in the catalyst layer. To do. Further, since the Ce-containing oxide particles usually have a secondary particle diameter of several μm, at least some of the Ce-containing oxide particles are dispersed and contacted with a plurality of fine iron oxide particles. And the amount of fine iron oxide particles attached to the Ce-containing oxide particles is relatively large. Thus, as will be apparent from the examples described later, according to the present invention, the NOx purification performance of the catalyst is enhanced, the sulfur poisoning resistance is increased, and the emission of NH 3 is further suppressed.
その理由は明確ではないが、上述の硝酸鉄から得られる酸化鉄粒子は、その粒径が500nm以上の大きな粒子であることから、Ce含有酸化物粒子との相互作用を発現し難いと考えられる。また、Ce含有酸化物粒子の表面ないし細孔に付着した硝酸鉄が、触媒焼成に伴って酸化鉄に変化し、凝集・粒成長することにより、さらにはその後の高温の排気ガスに晒されて凝集・粒成長することにより、Ce含有酸化物粒子の表面積の低下を招く、と推察される。 The reason for this is not clear, but the iron oxide particles obtained from the iron nitrate described above are large particles having a particle size of 500 nm or more, and therefore, it is considered difficult to express the interaction with the Ce-containing oxide particles. . In addition, iron nitrate adhering to the surface or pores of Ce-containing oxide particles is changed to iron oxide as the catalyst is fired, and is aggregated and grain-grown, and further exposed to high-temperature exhaust gas thereafter. It is presumed that the surface area of the Ce-containing oxide particles is reduced by agglomeration and grain growth.
これに対して、本発明の場合は、上述の如く粒径300nm以下の微細酸化鉄粒子がCe含有酸化物粒子及びNOxトラップ材各々に分散して接触しているから、Ce含有酸化物粒子やNOxトラップ材と酸化鉄粒子との相互作用を発現し易くなっていると考えられる。そのため、触媒金属量が少ない場合でも、その微細酸化鉄粒子がCe含有酸化物粒子と相俟って触媒層の酸素吸蔵放出能の向上に有効に働くと考えられる。また、Ce含有酸化物粒子に接触している微細酸化鉄粒子が該Ce含有酸化物粒子の塩基性を強くして、そのNOx吸着能を高め、NOxの還元浄化に有利になっていると考えられる。また、後にデータで説明するが、微細酸化鉄粒子は、硫黄成分の吸着及びNH3吸着にも寄与しており、そのため、NOxトラップ材の硫黄被毒が抑制され、さらに、NH3の排出が抑制される。従って、本発明に係る触媒はリーンNOx触媒として有用である。 On the other hand, in the case of the present invention, as described above, fine iron oxide particles having a particle size of 300 nm or less are dispersed and in contact with the Ce-containing oxide particles and the NOx trap material. It is considered that the interaction between the NOx trap material and the iron oxide particles is easily developed. Therefore, even when the amount of catalytic metal is small, it is considered that the fine iron oxide particles work together with the Ce-containing oxide particles to effectively improve the oxygen storage / release capacity of the catalyst layer. Further, it is considered that fine iron oxide particles in contact with Ce-containing oxide particles strengthen the basicity of the Ce-containing oxide particles, increase their NOx adsorption ability, and are advantageous for NOx reduction and purification. It is done. As will be described later in the data, the fine iron oxide particles contribute to the adsorption of sulfur components and the adsorption of NH 3. Therefore, sulfur poisoning of the NOx trap material is suppressed, and further, the emission of NH 3 is reduced. It is suppressed. Therefore, the catalyst according to the present invention is useful as a lean NOx catalyst.
上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は40%以上であることが好ましい。粒径50nm以上300nm以下の酸化鉄粒子についてみれば、酸化鉄粒子総面積に占める面積比率が40%以上95%以下程度であることが好ましい。 The area ratio of the fine iron oxide particles to the total iron oxide particle area is preferably 40% or more. In view of iron oxide particles having a particle size of 50 nm or more and 300 nm or less, the area ratio in the total area of the iron oxide particles is preferably about 40% or more and 95% or less.
上記微細酸化鉄粒子は、上記触媒層において上記Ce含有酸化物粒子等を上記担体に保持するバインダの少なくとも一部を構成するものとすることができる。すなわち、触媒一般におけるバインダについては次のように定義することができる。
A.バインダは、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒金属を担持する酸素吸蔵材、その他の助触媒粒子をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態に保持する。
The fine iron oxide particles may constitute at least a part of a binder that holds the Ce-containing oxide particles and the like on the carrier in the catalyst layer. That is, the binder in general catalysts can be defined as follows.
A. The binder uniformly disperses the oxygen storage material and other promoter particles supporting the catalyst metal in the slurry by imparting viscosity to the slurry to be coated on the carrier, and the washcoat layer before drying and firing is supported on the carrier. To keep it stable.
そのため、粒径が1nm〜50nm程度のコロイド粒子(水酸化物、含水物、酸化物等)が分散したコロイド溶液(市販のアルミナゾルやコロイダルシリカではコロイド粒子の粒径は10nm〜30nm程度)がバインダとして一般に使用される。
B.バインダは、上記乾燥・焼成後は微粒子となって触媒層に略均一に分散し、上記助触媒粒子間に介在して該助触媒粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする(アンカー効果)。
Therefore, a colloidal solution in which colloidal particles (hydroxide, hydrate, oxide, etc.) having a particle size of about 1 nm to 50 nm are dispersed (in the case of commercially available alumina sol or colloidal silica, the particle size of the colloidal particles is about 10 nm to 30 nm) is a binder. As commonly used.
B. The binder is finely dispersed in the catalyst layer after drying and firing, and is substantially uniformly dispersed in the catalyst layer. The binder is interposed between the promoter particles and bonds the promoter particles to each other. Enter the hole so that the catalyst layer does not peel from the carrier (anchor effect).
そのため、乾燥・焼成後において、助触媒粒子よりも粒径が小さな酸化物粒子となって助触媒粒子や担体に固着するものがバインダとして一般に使用される。
C.触媒層に、触媒金属やNOx吸蔵材、HC吸着材等が後から含浸担持されるケースでは、バインダはそれら触媒成分を担持するサポート材となる。
D.バインダ粒子間、バインダ粒子と助触媒粒子との間には排気ガスが通る微細孔が形成される。
E.触媒層におけるバインダ量は、一般には触媒層全体の5質量%〜20質量%とされる。
Therefore, what is fixed to the promoter particles or the carrier in the form of oxide particles having a particle diameter smaller than that of the promoter particles after drying and firing is generally used as the binder.
C. In the case where the catalyst layer is impregnated and supported with catalyst metal, NOx occlusion material, HC adsorbent, etc., the binder serves as a support material for supporting these catalyst components.
D. Micropores through which exhaust gas passes are formed between the binder particles and between the binder particles and the promoter particles.
E. The amount of binder in the catalyst layer is generally 5% by mass to 20% by mass of the entire catalyst layer.
本発明の場合、上記粒径300nm以下の微細酸化鉄粒子は、上記Ce含有酸化物粒子等の助触媒粒子の平均粒径(数μm程度)よりも小さく、上記触媒層に略均一に分散し、上記助触媒粒子間に介在して該助触媒粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする。このため、当該微細酸化鉄粒子は上記触媒層においてバインダとしての機能も発揮するものである。 In the case of the present invention, the fine iron oxide particles having a particle diameter of 300 nm or less are smaller than the average particle diameter (about several μm) of the promoter particles such as the Ce-containing oxide particles, and are dispersed substantially uniformly in the catalyst layer. The cocatalyst particles are bonded to each other by interposing between the cocatalyst particles, and the catalyst layer is prevented from peeling from the support by entering a large number of minute recesses or pores on the support surface. For this reason, the said fine iron oxide particle also exhibits the function as a binder in the said catalyst layer.
上記触媒層のバインダは、上記微細酸化鉄粒子のみで構成するようにしてよいが、安定な触媒層を得るために、この微細酸化鉄粒子の他に、遷移金属及び希土類金属から選ばれる少なくとも一種の金属の酸化物粒子(例えば、アルミナ粒子、ZrO2粒子、CeO2粒子等)をバインダとして含ませるようにしてもよい。このようなバインダ粒子(上記微細酸化鉄粒子及び上記金属酸化物粒子)は、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒成分をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態で保持することができるように、前駆体である金属化合物がそれぞれコロイド粒子として分散したゾルを原料とすることが好ましい。 The binder of the catalyst layer may be composed only of the fine iron oxide particles, but in order to obtain a stable catalyst layer, in addition to the fine iron oxide particles, at least one selected from transition metals and rare earth metals These metal oxide particles (for example, alumina particles, ZrO 2 particles, CeO 2 particles, etc.) may be included as a binder. Such binder particles (the fine iron oxide particles and the metal oxide particles) impart viscosity to the slurry to be coated on the carrier to uniformly disperse the catalyst component in the slurry, and before drying / calcination. It is preferable to use a sol in which the precursor metal compound is dispersed as colloidal particles, so that the washcoat layer can be stably held on the carrier.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることが好ましく、また、上記酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることが好ましい。 At least a part of the fine iron oxide particles is preferably hematite, and the iron oxide particles are preferably made from a sol in which maghemite, goethite and wustite are dispersed as colloidal particles.
また、上記NOxトラップ材としては、Baに代表されるアルカリ土類金属やアルカリ金属を採用することができる。 Moreover, as the NOx trap material, an alkaline earth metal typified by Ba or an alkali metal can be employed.
以上のように本発明によれば、担体上に、酸素吸蔵放出能をもつCe含有酸化物粒子と、該Ce含有酸化物粒子以外のNOxトラップ材と、触媒金属とを有する触媒層が形成されている排気ガス浄化用触媒において、上記触媒層には、上記Ce含有酸化物粒子及びNOxトラップ材に接触する粒径300nm以下の微細酸化鉄粒子が多数分散して含まれているから、触媒のNOx浄化性能が高くなるとともに、耐硫黄被毒性が高まり、さらに、NH3の排出が抑制される。 As described above, according to the present invention, a catalyst layer including Ce-containing oxide particles having oxygen storage / release ability, a NOx trap material other than the Ce-containing oxide particles, and a catalyst metal is formed on the support. In the exhaust gas purifying catalyst, the catalyst layer contains a large number of fine iron oxide particles having a particle size of 300 nm or less in contact with the Ce-containing oxide particles and the NOx trap material. While NOx purification performance is enhanced, sulfur poisoning resistance is increased, and further, NH 3 emissions are suppressed.
以下、本発明の実施形態を図面に基づいて説明する。尚、以下の好ましい実施形態の説明は、本質的に例示に過ぎず、本発明、その適用物或いはその用途を制限することを意図するものではない。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature and is not intended to limit the present invention, its application, or its use.
図1に、本発明に係る排気ガス浄化用触媒の一例として、自動車の排気ガス中のNOxを浄化するリーンNOx触媒(NOx吸蔵還元型触媒)を模式的に示す。同図において、1は無機酸化物によるハニカム担体のセル壁、2はセル壁1に形成された触媒層である。触媒層2は、酸素吸蔵放出能を持つCe含有酸化物粒子3と、バインダ粒子4と、Fe以外の触媒金属5とを有し、図例では、Ce含有酸化物粒子3以外の助触媒粒子として、さらにアルミナ粒子6及びNOxトラップ材8を有する。なお、触媒層2には、Ce含有酸化物粒子3及びアルミナ粒子6以外に、NOx吸蔵材など他の助触媒粒子を含ませることができる。バインダ粒子4は、Ce含有酸化物粒子3及びアルミナ粒子6各々の平均粒径よりも小さな金属酸化物粒子よりなり、少なくとも一部のバインダ粒子4は粒径300nm以下の微細酸化鉄粒子で構成されている。すなわち、当該微細酸化鉄粒子と他の金属酸化物粒子とを組み合わせてバインダとすることもできる。 FIG. 1 schematically shows a lean NOx catalyst (NOx occlusion reduction type catalyst) that purifies NOx in automobile exhaust gas as an example of an exhaust gas purification catalyst according to the present invention. In the figure, 1 is a cell wall of a honeycomb carrier made of an inorganic oxide, and 2 is a catalyst layer formed on the cell wall 1. The catalyst layer 2 includes Ce-containing oxide particles 3 having oxygen storage / release ability, binder particles 4 and catalyst metals 5 other than Fe. In the illustrated example, promoter particles other than Ce-containing oxide particles 3 are used. As a further example, alumina particles 6 and a NOx trap material 8 are included. In addition to the Ce-containing oxide particles 3 and the alumina particles 6, the catalyst layer 2 can contain other promoter particles such as a NOx storage material. The binder particles 4 are made of metal oxide particles smaller than the average particle size of each of the Ce-containing oxide particles 3 and the alumina particles 6, and at least some of the binder particles 4 are composed of fine iron oxide particles having a particle size of 300 nm or less. ing. That is, the fine iron oxide particles and other metal oxide particles can be combined to form a binder.
上記微細酸化鉄粒子を含むバインダ粒子4は、触媒層2の全体にわたって略均一に分散していて、助触媒粒子(Ce含有酸化物粒子3、アルミナ粒子6等)間に介在し該助触媒粒子同士を結合している。従って、少なくとも一部の微細酸化鉄粒子はCe含有酸化物粒子3に接触している。また、上記バインダ粒子4は、担体セル壁1の表面ポア(微小凹部ないし細孔)7に充填され、アンカー効果によって触媒層2をセル壁1に保持している。触媒金属5は助触媒粒子(Ce含有酸化物粒子3、アルミナ粒子6等)に担持されている。 The binder particles 4 containing the fine iron oxide particles are substantially uniformly dispersed throughout the catalyst layer 2, and are interposed between the promoter particles (Ce-containing oxide particles 3, alumina particles 6, etc.). They are connected to each other. Accordingly, at least some of the fine iron oxide particles are in contact with the Ce-containing oxide particles 3. The binder particles 4 are filled in the surface pores (microscopic recesses or pores) 7 of the carrier cell wall 1 and hold the catalyst layer 2 on the cell wall 1 by an anchor effect. The catalyst metal 5 is supported on promoter particles (Ce-containing oxide particles 3, alumina particles 6 and the like).
<触媒の調製>
エタノール100mL当たり硝酸第二鉄40.4gを溶かし、90℃から100℃の温度で2時間から3時間の還流を行なうことによって、スラリー状の液体、すなわち、酸化鉄ゾル(バインダ)を得る。Ce含有酸化物粉末及び他の助触媒材料を混合し、これに酸化鉄ゾル及びイオン交換水を適量混合してスラリーとする。必要に応じて、他のバインダを添加する。上記スラリーを担体にコーティングし、乾燥及び焼成を施す。担体上にコーティング層に、触媒金属溶液、並びにNOxトラップ材となるアルカリ土類金属等の溶液を含浸させ、乾燥及び焼成を行なう。以上により排気ガス浄化用触媒(リーンNOx触媒)が得られる。
<Preparation of catalyst>
By dissolving 40.4 g of ferric nitrate per 100 mL of ethanol and refluxing at a temperature of 90 ° C. to 100 ° C. for 2 to 3 hours, a slurry-like liquid, that is, an iron oxide sol (binder) is obtained. Ce-containing oxide powder and other promoter material are mixed, and an appropriate amount of iron oxide sol and ion-exchanged water is mixed with this to form a slurry. If necessary, other binder is added. The slurry is coated on a carrier, dried and fired. A coating layer is impregnated with a catalyst metal solution and a solution of an alkaline earth metal or the like serving as a NOx trap material on the support, followed by drying and firing. Thus, an exhaust gas purification catalyst (lean NOx catalyst) is obtained.
<酸化鉄粒子の粒径等>
上記酸化鉄ゾルとCe含有酸化物粉末としてのCeZrNd複合酸化物(CeO2:ZrO2:Nd2O3=23:67:10(質量比))とイオン交換水とを混合することによりスラリーを調製し、このスラリーを基材にコーティングし、乾燥(150℃)及び焼成(大気中において500℃の温度に2時間保持)を行なうことにより、触媒材を得た。酸化鉄ゾルとCeZrNd複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とCeZrNd複合酸化物とが2:8となるように混合した。
<Iron oxide particle size>
The slurry was prepared by mixing the iron oxide sol and CeZrNd composite oxide (CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio)) as Ce-containing oxide powder and ion-exchanged water. The catalyst material was obtained by preparing, coating this slurry on a base material, and performing drying (150 ° C.) and firing (maintaining at a temperature of 500 ° C. for 2 hours in the air). The iron oxide sol and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図2は得られた触媒材の透過電子顕微鏡を用いたSTEM(走査透過)像、図3乃至図5はFe、Zr及びCe各原子の相対濃度分布をマッピングしたものである。図2乃至図5から、CeZrNd複合酸化物粒子の粒径は1μm程度であること、酸化鉄粒子は粒径が300nm以下であり、50nm以上300nm以下の大きさの複数個の酸化鉄粒子がCeZrNd複合酸化物粒子に接触(粒子上に分布)していることがわかる。この場合、当該顕微鏡観察において、粒径300nm以下の微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は100%である(つまり、全ての酸化鉄粒子が粒径300nm以下である)ということができる。 FIG. 2 is an STEM (scanning transmission) image of the obtained catalyst material using a transmission electron microscope, and FIGS. 3 to 5 are maps of relative concentration distributions of Fe, Zr and Ce atoms. From FIG. 2 to FIG. 5, the particle size of the CeZrNd composite oxide particles is about 1 μm, the iron oxide particles have a particle size of 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm or more and 300 nm or less are CeZrNd. It can be seen that the composite oxide particles are in contact (distributed on the particles). In this case, in the microscopic observation, the area ratio of fine iron oxide particles having a particle diameter of 300 nm or less to the total area of iron oxide particles is 100% (that is, all iron oxide particles have a particle diameter of 300 nm or less). Can do.
図6乃至図9は上記触媒材のエージング(酸素を2%、水蒸気を10%含む窒素ガス中で900℃の温度に24時間保持)後でのSTEM像及び各原子の相対濃度分布のマッピングである。CeZrNd複合酸化物粒子の粒径は1μm程度であり、酸化鉄粒子の粒径は300nm以下であり、50nm以上300nm以下の大きさの酸化鉄粒子がCeZrNd複合酸化物粒子に複数個接触(粒子上に分布)している。エージング後においても、当該電子顕微鏡観察によれば、全ての酸化鉄粒子の粒径が300nm以下になっている。 6 to 9 are mappings of the STEM image and the relative concentration distribution of each atom after aging of the above catalyst material (held at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). is there. The particle size of the CeZrNd composite oxide particles is about 1 μm, the particle size of the iron oxide particles is 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm to 300 nm are in contact with the CeZrNd composite oxide particles (on the particle Distributed). Even after aging, according to the observation with the electron microscope, the particle diameter of all iron oxide particles is 300 nm or less.
図10は酸化鉄ゾルを150℃で乾燥したもの(乾燥品)、上記エージング前の触媒材(焼成品)、並びに上記エージング後の触媒材(焼成・エージング品)各々のX線回折チャートである。なお、同図の「OSC」は上記CeZrNd複合酸化物のことを意味する(この点は他の図面でも同様である。)。酸化鉄ゾルは、マグヘマイト(γ-Fe2O3)、ゲータイト(Fe3+O(OH))及びウスタイト(FeO)がコロイド粒子として分散したものであることがわかる。そして、酸化鉄ゾルのコロイド粒子は焼成によってヘマタイト(α-Fe2O3)になっている。 FIG. 10 is an X-ray diffraction chart of the iron oxide sol dried at 150 ° C. (dried product), the catalyst material before aging (fired product), and the catalyst material after aging (fired / aged product). . In addition, “OSC” in the figure means the CeZrNd composite oxide (this is the same in other drawings). It can be seen that the iron oxide sol is one in which maghemite (γ-Fe 2 O 3 ), goethite (Fe 3+ O (OH)) and wustite (FeO) are dispersed as colloidal particles. The colloidal particles of the iron oxide sol are converted into hematite (α-Fe 2 O 3 ) by firing.
上記エージング前の焼成品におけるヘマタイトの、結晶面(104)のピーク強度を100とする各結晶面の相対ピーク強度は表1に示す通りである。また、上記エージング後のヘマタイトの、結晶面(104)のピーク強度を100とする各結晶面の相対ピーク強度は表2に示す通りである。なお、表中「−」はピーク重複や、ピーク小のために、正確な数値が得られなかったものである。 Table 1 shows the relative peak intensities of the crystal faces of hematite in the fired product before aging, with the peak intensity of the crystal face (104) being 100. Further, the relative peak intensity of each crystal plane with the peak intensity of the crystal plane (104) of the hematite after aging as 100 is shown in Table 2. Note that “−” in the table indicates that an exact numerical value could not be obtained due to peak overlap or small peak.
エージング後において、X線回折測定によって得られるヘマタイトの各結晶面のピーク強度は、結晶面(104)、結晶面(110)、結晶面(116)の順で小さくなっている。 After aging, the peak intensity of each crystal plane of hematite obtained by X-ray diffraction measurement decreases in the order of crystal plane (104), crystal plane (110), and crystal plane (116).
一方、比較のために、上記酸化鉄ゾルに代えて、硝酸第二鉄水溶液を上記CeZrNd複合酸化物粉末に含浸させ、同様の乾燥及び焼成を行なった。硝酸第二鉄とCeZrNd複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とCeZrNd複合酸化物とが2:8となるように混合した。 On the other hand, for comparison, the CeZrNd composite oxide powder was impregnated with the ferric nitrate aqueous solution instead of the iron oxide sol, and the same drying and firing were performed. The ferric nitrate and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図11乃至図14は得られた上記硝酸第二鉄による触媒材のSTEM像及び各原子の相対濃度分布のマッピングである。CeZrNd複合酸化物粒子の粒径は1μm程度であるが、酸化鉄粒子の粒径は600〜700nm程度になっている。 FIG. 11 to FIG. 14 are mapping of the obtained STEM image of the catalyst material by ferric nitrate and the relative concentration distribution of each atom. The particle size of CeZrNd composite oxide particles is about 1 μm, while the particle size of iron oxide particles is about 600 to 700 nm.
図15乃至図18は上記硝酸第二鉄による触媒材のエージング(酸化鉄ゾルの場合と同じ条件)後でのSTEM像及び各原子の相対濃度分布のマッピングである。CeZrNd複合酸化物粒子の粒径は1.5〜2μm程度であるが、酸化鉄粒子としては、粒径が600〜700nm程度の粒子が1個と、100nm程度の粒子が3個見られる。当該電子顕微鏡観察において、粒径300nm以下の酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は10%未満である。 15 to 18 are STEM images after mapping of the catalyst material with ferric nitrate (same conditions as in the case of iron oxide sol) and mapping of the relative concentration distribution of each atom. The particle size of the CeZrNd composite oxide particles is about 1.5 to 2 μm. As the iron oxide particles, one particle having a particle size of about 600 to 700 nm and three particles of about 100 nm are seen. In the electron microscope observation, the area ratio of the iron oxide particles having a particle size of 300 nm or less to the total iron oxide particle area is less than 10%.
上記酸化鉄ゾルの場合、焼成によって酸化鉄粒子となるコロイド粒子(マグヘマイト、ゲータイト及びウスタイト)が比較的安定なFe化合物であり、そのために、酸化鉄粒子の粒成長を生じ難い。これに対して、上記硝酸第二鉄の場合は、反応性が高いFeイオンから酸化鉄粒子を生ずるから、粒成長し易い。このことが、上記酸化鉄ゾルから得られる酸化鉄粒子と上記硝酸第二鉄から得られる酸化鉄粒子の粒径の差違となっていると考えられる。 In the case of the iron oxide sol, colloidal particles (maghemite, goethite, and wustite) that become iron oxide particles upon firing are relatively stable Fe compounds, and therefore, iron oxide particle growth hardly occurs. On the other hand, in the case of ferric nitrate, iron oxide particles are generated from highly reactive Fe ions, so that the grains are easily grown. This is considered to be the difference in particle diameter between the iron oxide particles obtained from the iron oxide sol and the iron oxide particles obtained from the ferric nitrate.
<酸素吸蔵放出能>
上記酸化鉄ゾルを用いて調製した触媒サンプルAと、上記硝酸第二鉄を用いて調製した触媒サンプルBと、鉄成分を含まない触媒サンプルCとについて、各々の酸素吸蔵放出能を調べた。但し、いずれのサンプルも触媒金属量は零とした。
<Oxygen storage and release ability>
Each of the catalyst samples A prepared using the iron oxide sol, the catalyst sample B prepared using the ferric nitrate, and the catalyst sample C containing no iron component were examined for oxygen storage / release capacity. However, the amount of catalyst metal in all samples was zero.
−触媒サンプルAの調製−
上記CeZrNd複合酸化物と上記酸化鉄ゾルとZrO2バインダとイオン交換水とを混合することによりスラリーを調製し、このスラリーを担体にコーティングし、乾燥(150℃)及び焼成(大気中において500℃の温度に2時間保持)を行なった。上記スラリーは、上記CeZrNd複合酸化物の担持量が80g/L、上記酸化鉄ゾルによる酸化鉄の担持量が20g/L、上記ZrO2バインダによるZrO2の担持量が10g/Lとなるように調製した。なお、各担持量は上記焼成後における上記担体1L当たりの各成分の量である。担体としては、セル壁厚さ3.5mil(8.89×10−2mm)、1平方インチ(645.16mm2)当たりのセル数600のコージェライト製ハニカム担体(容量25mL)を採用した。
-Preparation of catalyst sample A-
A slurry is prepared by mixing the CeZrNd composite oxide, the iron oxide sol, the ZrO 2 binder, and ion-exchanged water. The slurry is coated on a support, dried (150 ° C.) and fired (500 ° C. in the air). For 2 hours). The slurry is such that the supported amount is 80 g / L of the CeZrNd mixed oxide, the supported amount of iron oxide by the iron oxide sol 20 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared. Each supported amount is the amount of each component per 1 L of the carrier after the firing. As the carrier, a cordierite honeycomb carrier (capacity: 25 mL) having a cell wall thickness of 3.5 mil (8.89 × 10 −2 mm) and 600 cells per square inch (645.16 mm 2 ) was employed.
−触媒サンプルBの調製−
上記酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用し、他は触媒サンプルAと同じ条件で第2触媒サンプル2を調製した。硝酸第二鉄水溶液による酸化鉄担持量は触媒サンプルAの上記酸化鉄ゾルによる酸化鉄担持量と同じく、20g/Lである。
-Preparation of catalyst sample B-
Instead of the iron oxide sol, a ferric nitrate aqueous solution was employed, and a second catalyst sample 2 was prepared under the same conditions as in catalyst sample A. The amount of iron oxide supported by the ferric nitrate aqueous solution is 20 g / L, the same as the amount of iron oxide supported by the iron oxide sol of catalyst sample A.
−触媒サンプルCの調製−
上記酸化鉄ゾルを用いず(酸化鉄担持量=0g/L)、上記CeZrNd複合酸化物担持量が100g/L、上記ZrO2バインダによるZrO2の担持量が10g/Lとなるようにする他は、触媒サンプルAと同じ条件で触媒サンプルCを調製した。
-Preparation of catalyst sample C-
Other to make without using the iron oxide sol (iron oxide supported amount = 0g / L), the CeZrNd mixed oxide support amount was 100 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared catalyst sample C under the same conditions as catalyst sample A.
−酸素吸蔵放出能の評価−
図19は、酸素吸蔵放出量を測定するための試験装置の構成を示す。同図において、符号11は触媒サンプル12を保持するガラス管であり、触媒サンプル12はヒータ13によって所定温度に加熱保持される。ガラス管11の触媒サンプル12よりも上流側には、ベースガスN2を供給しながらO2及びCOの各ガスをパルス状に供給可能なパルスガス発生装置14が接続され、ガラス管11の触媒サンプル12よりも下流側には排気部18が設けられている。ガラス管11の触媒サンプル12よりも上流側及び下流側にはA/Fセンサ(酸素センサ)15,16が設けられている。ガラス管11のサンプル保持部には温度制御用の熱電対19が取付けられている。
-Evaluation of oxygen storage capacity-
FIG. 19 shows the configuration of a test apparatus for measuring the oxygen storage / release amount. In the figure, reference numeral 11 denotes a glass tube that holds a catalyst sample 12, and the catalyst sample 12 is heated and held at a predetermined temperature by a heater 13. Connected to the upstream side of the catalyst sample 12 of the glass tube 11 is a pulse gas generator 14 capable of supplying O 2 and CO gases in pulses while supplying the base gas N 2. An exhaust unit 18 is provided on the downstream side of 12. A / F sensors (oxygen sensors) 15 and 16 are provided upstream and downstream of the catalyst sample 12 of the glass tube 11. A temperature control thermocouple 19 is attached to the sample holder of the glass tube 11.
測定にあたっては、ガラス管11内の触媒サンプル温度を所定値に保ち、ベースガスN2を供給して排気部18から排気しながら、図20に示すようにO2パルス(20秒)とCOパルス(20秒)とを交互に且つ間隔(20秒)をおいて発生させることにより、リーン→ストイキ→リッチ→ストイキのサイクルを繰り返すようにした。ストイキからリッチに切り換えた直後から、図21に示すように、触媒サンプル前後のA/Fセンサ15,16によって得られるA/F値出力差(前側A/F値−後側A/F値)がなくなるまでの時間における、当該出力差をO2量に換算し、これを触媒サンプルのO2放出量(酸素吸蔵放出量)とした。このO2放出量を200℃から600℃までの50℃刻みの各温度で測定した。 In the measurement, the catalyst sample temperature in the glass tube 11 is kept at a predetermined value, the base gas N 2 is supplied and exhausted from the exhaust unit 18, and as shown in FIG. 20, an O 2 pulse (20 seconds) and a CO pulse By alternately generating (20 seconds) and intervals (20 seconds), the cycle of lean → stoichi → rich → stoichi was repeated. Immediately after switching from stoichiometric to rich, as shown in FIG. 21, the A / F value output difference (front A / F value−rear A / F value) obtained by the A / F sensors 15 and 16 before and after the catalyst sample. The output difference in the time until disappearance is converted into an O 2 amount, and this is defined as an O 2 release amount (oxygen occlusion release amount) of the catalyst sample. The amount of released O 2 was measured at each temperature in increments of 50 ° C. from 200 ° C. to 600 ° C.
結果を図22に示す。触媒サンプルA(酸化鉄ゾル+OSC)及び触媒サンプルB(硝酸第二鉄+OSC)のいずれも、酸化鉄を含まない触媒サンプルC(OSCのみ)よりも酸素放出量が多くなっている。(酸化鉄ゾル+OSC)と(硝酸第二鉄+OSC)とを比較すると、250℃〜600℃において、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多くなっている。 The results are shown in FIG. Both the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) have a larger oxygen release amount than the catalyst sample C not containing iron oxide (OSC only). When comparing (iron oxide sol + OSC) and (ferric nitrate + OSC), the amount of oxygen released from iron oxide sol is larger than that from ferric nitrate at 250 ° C. to 600 ° C.
図23は(酸化鉄ゾル+OSC)及び(硝酸第二鉄+OSC)の各触媒サンプルのエージング(酸素を2%、水蒸気を10%含む窒素ガス中で900℃の温度に24時間保持)後の酸素放出量を測定した結果を示す。いずれもエージング後は酸素放出量が少なくなっているが、それでも、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多い。 FIG. 23 shows oxygen after aging of each of (iron oxide sol + OSC) and (ferric nitrate + OSC) catalyst samples (held at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). The result of measuring the release amount is shown. In both cases, the amount of oxygen released after aging is reduced, but the iron oxide sol still has a higher amount of released oxygen than ferric nitrate.
触媒サンプルAの場合は、酸化鉄ゾルによる複数の粒径300nm以下の酸化鉄粒子がCeZrNd複合酸化物(OSC)粒子に分散して接触しており(図2乃至図5参照)、そのため、それら酸化鉄粒子がCeZrNd複合酸化物粒子と相俟って触媒の酸素吸蔵放出能の向上に有効に働いているものと認められる。これに対して、触媒サンプルBの場合は、硝酸第二鉄による酸化鉄粒子の粒径が大きく(図11乃至図14参照)、そのため、酸化鉄粒子による酸素吸蔵放出能の向上が酸化鉄ゾルによるものに比べて低いものと認められる。 In the case of the catalyst sample A, a plurality of iron oxide particles having a particle size of 300 nm or less made of iron oxide sol are dispersed and in contact with CeZrNd composite oxide (OSC) particles (see FIGS. 2 to 5). It is recognized that the iron oxide particles work together with the CeZrNd composite oxide particles to effectively improve the oxygen storage / release capability of the catalyst. On the other hand, in the case of the catalyst sample B, the particle size of the iron oxide particles due to ferric nitrate is large (see FIGS. 11 to 14). It is recognized that it is lower than that by
図24は上記エージング後の触媒サンプルA(酸化鉄ゾル+OSC)及び触媒サンプルB(硝酸第二鉄+OSC)の酸素放出量(測定温度500℃)を、従来触媒及び実施例触媒各々の当該エージング後の酸素放出量(測定温度500℃)と共に示すグラフである。従来触媒は、上記触媒サンプルC(OSCのみ)においてそのCeZrNd複合酸化物粒子に触媒金属としてPtを1g/L担持させたものである。実施例触媒は、上記触媒サンプルA(酸化鉄ゾル+OSC)においてそのCeZrNd複合酸化物粒子に触媒金属としてPtを1g/L担持させたものである。 FIG. 24 shows the oxygen release amounts (measurement temperature 500 ° C.) of the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) after the aging after the aging of the conventional catalyst and the example catalyst, respectively. It is a graph shown with the amount of oxygen release (measurement temperature 500 degreeC). The conventional catalyst is obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles in the catalyst sample C (OSC only). In the catalyst sample A (iron oxide sol + OSC), the catalyst of the example was obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles.
触媒サンプルA(酸化鉄ゾル+OSC)は、触媒金属PtをCeZrNd複合酸化物粒子に担持させていないにも拘わらず、CeZrNd複合酸化物粒子に触媒金属Ptを担持させた従来触媒と同程度の酸素放出量になっている。また、触媒サンプルAにおいてCeZrNd複合酸化物粒子に触媒金属Ptを担持させた実施例触媒は、従来触媒に比べて酸素放出量が格段に多くなっている。これらから、酸化鉄ゾルによる粒径の小さな酸化鉄粒子が酸素吸蔵放出能の向上に大きな効果を示すことがわかる。 The catalyst sample A (iron oxide sol + OSC) has the same level of oxygen as the conventional catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles even though the catalyst metal Pt is not supported on the CeZrNd composite oxide particles. The amount is released. Further, in the catalyst sample A, the example catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles has a much larger oxygen release amount than the conventional catalyst. From these, it can be seen that the iron oxide particles having a small particle diameter by the iron oxide sol have a great effect in improving the oxygen storage / release ability.
<NO吸着能及びNH3吸着能>
Ce含有酸化物系触媒材料(実施例材料A,比較例材料B,比較例材料C)を調製し、各々のNOx吸着能及びNH3吸着能を評価した。
<NO adsorption capacity and NH 3 adsorption capacity>
Ce-containing oxide-based catalyst materials (Example material A, Comparative example material B, Comparative example material C) were prepared, and their NOx adsorption ability and NH 3 adsorption ability were evaluated.
−実施例材料A−
CeZr複合酸化物粉末(CeO2:ZrO2=90:10(質量比))40gに、上記酸化鉄ゾル及び水を混合し、150℃の温度に2時間保持する乾燥、並びに500℃の温度に2時間保持する焼成を行なうことにより、実施例材料Aを得た。酸化鉄ゾルの混合量は、焼成によって得られる酸化鉄量が8gとなるように調整した。
-Example material A-
The iron oxide sol and water are mixed with 40 g of CeZr composite oxide powder (CeO 2 : ZrO 2 = 90: 10 (mass ratio)), dried at a temperature of 150 ° C. for 2 hours, and heated to a temperature of 500 ° C. Example material A was obtained by baking for 2 hours. The amount of iron oxide sol mixed was adjusted so that the amount of iron oxide obtained by firing was 8 g.
−比較例材料B−
酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用する他は実施例材料Aと同じ条件で比較例材料Bを得た。硝酸第二鉄による酸化鉄量は、実施例材料Aと同じく、8gとなるようにした。
-Comparative Example Material B-
Comparative Example Material B was obtained under the same conditions as Example Material A, except that an aqueous ferric nitrate solution was used instead of the iron oxide sol. The amount of iron oxide by ferric nitrate was set to 8 g as in Example material A.
−比較例材料C−
酸化鉄ゾルに代えてアルミナゾルを採用する他は実施例材料Aと同じ条件で比較例材料Cを得た。但し、CeZr複合酸化物粉末量は48gとし、アルミナゾルによるアルミナ量は9.6gとなるようにした。
-Comparative material C-
Comparative Example Material C was obtained under the same conditions as Example Material A, except that alumina sol was used instead of iron oxide sol. However, the CeZr composite oxide powder amount was 48 g, and the alumina amount by alumina sol was 9.6 g.
−NO吸着量の測定−
上記実施例及び比較例の各触媒材料A,B,C各々0.05gを準備し、ガス流通反応装置及びガス分析装置を用いて、プリコンディショニングを行なった後、NO吸着量を測定した。プリコンディショニングは、試料をHe気流中で600℃の温度に10分間保持するというものである。次いで、モデルガス(NO;5000ppm,O2;5%,残He)を100mL/分の流量で流しながら、ガス温度を室温から600℃まで上昇させ、その間に吸着されたNO成分量を算出して、NO吸着量とした。
-Measurement of NO adsorption amount-
0.05 g of each of the catalyst materials A, B, and C of the above Examples and Comparative Examples was prepared, preconditioned using a gas flow reactor and a gas analyzer, and then the NO adsorption amount was measured. Preconditioning is to hold the sample at a temperature of 600 ° C. for 10 minutes in a He stream. Next, while flowing the model gas (NO; 5000 ppm, O 2 ; 5%, remaining He) at a flow rate of 100 mL / min, the gas temperature is increased from room temperature to 600 ° C., and the amount of NO components adsorbed during that time is calculated. Thus, the NO adsorption amount was used.
−NH3吸着量の測定−
上記実施例及び比較例の各触媒材料A,B,C各々0.05gを準備し、それぞれガス流通反応装置及びガス分析装置を用いて、NO吸着量の測定の場合と同じプリコンディショニングを行なった後、NH3吸着量を測定した。
-Measurement of NH 3 adsorption amount-
0.05 g of each of the catalyst materials A, B, and C of the above Examples and Comparative Examples was prepared, and the same preconditioning as that in the case of measuring the NO adsorption amount was performed using a gas flow reactor and a gas analyzer, respectively. Then, the amount of NH 3 adsorption was measured.
NH3吸着量の測定にあたっては、モデルガス(NH3;2%,残He)を温度100℃、100mL/分の流量で流してNH3を試料に吸着させ、次いで、NH3濃度0%のHeガスに切り換えて、100℃から600℃まで、10℃/分の速度で昇温し、このときに、試料を通過したガス中に含まれるNH3量を算出してNH3吸着量とした。 In measuring the NH 3 adsorption amount, a model gas (NH 3 ; 2%, remaining He) was flowed at a temperature of 100 ° C. and a flow rate of 100 mL / min to adsorb NH 3 to the sample, and then the NH 3 concentration was 0%. Switching to He gas, the temperature was raised from 100 ° C. to 600 ° C. at a rate of 10 ° C./min. At this time, the amount of NH 3 contained in the gas that passed through the sample was calculated and used as the NH 3 adsorption amount .
−結果−
結果を図25に示す。酸化鉄ゾルを採用した実施例材料AではNO吸着量が110×10−5mol/g以上あるのに対して、比較例材料B,CではNO吸着量が極めて少ない。NH3吸着量に関しても、実施例材料Aは比較例材料B,Cよりも多くなっている。実施例材料AのNO吸着量が顕著に多いのは、酸化鉄ゾルによる微細酸化鉄粒子がCe含有酸化物の塩基性を強くしたためと考えられる。実施例材料AのNH3吸着量が多いのは、酸化鉄ゾルによる微細酸化鉄粒子がNH3の吸着に関与しているためである。
-Result-
The results are shown in FIG. In the example material A employing the iron oxide sol, the NO adsorption amount is 110 × 10 −5 mol / g or more, whereas in the comparative material B and C, the NO adsorption amount is extremely small. Regarding the NH 3 adsorption amount, the example material A is larger than the comparative example materials B and C. The reason why the NO adsorption amount of Example Material A is remarkably large is considered that the fine iron oxide particles by the iron oxide sol strengthened the basicity of the Ce-containing oxide. The reason why the amount of NH 3 adsorbed in Example Material A is large is that fine iron oxide particles by the iron oxide sol are involved in the adsorption of NH 3 .
以上の結果から、酸化鉄ゾルによる微細酸化鉄粒子を触媒層に分散させると、触媒のNOx浄化性能が高まること、並びに吸蔵したNOxを脱離させて還元したときに、NH3が多く発生しても、該NH3の排出が少なくなることがわかる。 From the above results, when fine iron oxide particles made of iron oxide sol are dispersed in the catalyst layer, the NOx purification performance of the catalyst is increased, and a large amount of NH 3 is generated when the stored NOx is desorbed and reduced. However, it can be seen that the emission of NH 3 is reduced.
<リーンNOx浄化性能>
次の実施例及び比較例1,2のリーンNOx触媒を調製し、エージング後のリーンNOx浄化率、耐硫黄被毒性、硫黄被毒からの回復性を評価した。
<Lean NOx purification performance>
The lean NOx catalysts of the following examples and comparative examples 1 and 2 were prepared, and the lean NOx purification rate, sulfur poisoning resistance, and recoverability from sulfur poisoning after aging were evaluated.
−実施例−
γ−アルミナ粉末とCeZr複合酸化物粉末(CeO2:ZrO2=75:25(質量比))とを混合し、これにバインダとしての上記酸化鉄ゾル及びイオン交換水を混合することによりスラリーを調製し、このスラリーを担体にコーティングし、乾燥(150℃の温度に2時間保持)及び焼成(大気中において500℃の温度に2時間保持)を行なった。次いで、酢酸バリウム及び酢酸ストロンチウムをイオン交換水に溶かし、その溶液とジニトロジアンミン白金硝酸溶液と硝酸ロジウム溶液とを混合した。この混合溶液を上記担体のコーティング層に含浸させ、乾燥(150℃の温度に2時間保持)及び焼成(大気中において500℃の温度に2時間保持を行なうことにより、実施例に係る触媒を得た。
-Example-
A slurry is prepared by mixing γ-alumina powder and CeZr composite oxide powder (CeO 2 : ZrO 2 = 75: 25 (mass ratio)), and mixing the iron oxide sol and ion-exchanged water as a binder. The slurry was prepared, coated on the support, dried (held at a temperature of 150 ° C. for 2 hours) and fired (held at a temperature of 500 ° C. for 2 hours in the air). Next, barium acetate and strontium acetate were dissolved in ion exchange water, and the solution, dinitrodiammine platinum nitrate solution, and rhodium nitrate solution were mixed. This mixed solution is impregnated into the coating layer of the carrier, dried (kept at 150 ° C. for 2 hours) and calcined (kept at 500 ° C. in the atmosphere for 2 hours) to obtain the catalyst according to the example. It was.
当該触媒は、γ−アルミナ担持量が120g/L、CeZr複合酸化物担持量が120g/L、Ba担持量が30g/L、Sr担持量が3g/L、Pt担持量が2g/L、Rh担持量が0.3g/L、酸化鉄ゾルによる酸化鉄担持量が24g/Lである。なお、各担持量は上記焼成後における上記担体1L当たりの各成分の量である。また、担体としては、セル壁厚さ4mil(10.16×10−2mm)、1平方インチ(645.16mm2)当たりのセル数400のコージェライト製ハニカム担体(容量55mL)を採用した。 The catalyst has a γ-alumina loading of 120 g / L, a CeZr composite oxide loading of 120 g / L, a Ba loading of 30 g / L, a Sr loading of 3 g / L, a Pt loading of 2 g / L, and Rh. The supported amount is 0.3 g / L, and the supported amount of iron oxide by the iron oxide sol is 24 g / L. Each supported amount is the amount of each component per 1 L of the carrier after the firing. As the carrier, a cordierite honeycomb carrier (capacity 55 mL) having a cell wall thickness of 4 mil (10.16 × 10 −2 mm) and 400 cells per square inch (645.16 mm 2 ) was employed.
−比較例1−
酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用する他は実施例と同じ条件で比較例1に係る触媒を調製した。硝酸第二鉄による酸化鉄担持量は24g/Lである。
-Comparative Example 1-
A catalyst according to Comparative Example 1 was prepared under the same conditions as in the Examples except that a ferric nitrate aqueous solution was used instead of the iron oxide sol. The amount of iron oxide supported by ferric nitrate is 24 g / L.
−比較例2−
酸化鉄ゾルに代えてアルミナゾルを採用する他は実施例と同じ条件で比較例2に係る触媒を調製した。アルミナゾルによるアルミナ担持量は24g/Lである。
-Comparative Example 2-
A catalyst according to Comparative Example 2 was prepared under the same conditions as in Examples except that alumina sol was used instead of iron oxide sol. The amount of alumina supported by the alumina sol is 24 g / L.
−リーンNOx浄化性能評価−
上記実施例及び比較例1,2の各触媒について、800℃の大気雰囲気に20時間保持するエージングを行なった後、モデルガス流通反応装置及び排気ガス分析装置を用いてリーンNOx浄化性能を調べた。すなわち、リーン(A/F=22)のモデル排気ガスを60秒間流し、次にガス組成をリッチ(A/F=14.5)のモデル排気ガスに切り換えてこれを60秒間流す、というサイクルを数回繰り返した後、ガス組成をリッチからリーンに切り換えた時点から60秒間のNOx浄化率(リーンNOx浄化率)を測定した。リーンモデル排気ガス及びリッチのモデル排気ガスの組成は表3に示すとおりであり、空間速度は35000/hとした。
-Lean NOx purification performance evaluation-
For each of the catalysts in Examples and Comparative Examples 1 and 2, after performing aging for 20 hours in an air atmosphere at 800 ° C., the lean NOx purification performance was examined using a model gas flow reactor and an exhaust gas analyzer. . That is, a cycle in which lean (A / F = 22) model exhaust gas is flowed for 60 seconds, then the gas composition is switched to rich (A / F = 14.5) model exhaust gas, and this is flowed for 60 seconds. After repeating several times, the NOx purification rate (lean NOx purification rate) for 60 seconds was measured from the time when the gas composition was switched from rich to lean. The composition of the lean model exhaust gas and the rich model exhaust gas is as shown in Table 3, and the space velocity was 35000 / h.
触媒入口ガス温度180℃、300℃及び450℃でのリーンNOx浄化率を図26に示す。バインダとして酸化鉄ゾルを採用した実施例は、180℃、300℃及び450℃のいずれにおいても、比較例1,2よりもNOx浄化率が高い。酸化鉄ゾルによる微細酸化鉄粒子を触媒層に分散させると、低温から高温にわたる広い温度範囲でNOx浄化能が高まることがわかる。比較例1は、実施例と同じく、酸化鉄粒子が触媒層に分散しているものの、酸化鉄を含有しない比較例2よりも性能が悪くなっている。比較例1の場合、その酸化鉄粒子は硝酸第二鉄によるものであって、その粒径が大きいことから、CeZr複合酸化物の酸素吸蔵放出能及びNOx吸着能を高めるに至らず、かえって、酸化鉄粒子がCeZr複合酸化物粒子の比表面積を低下させて性能が悪くなったものと考えられる。 FIG. 26 shows lean NOx purification rates at catalyst inlet gas temperatures of 180 ° C., 300 ° C., and 450 ° C. The Example which employ | adopted iron oxide sol as a binder has a higher NOx purification rate than Comparative Examples 1 and 2 in any of 180 degreeC, 300 degreeC, and 450 degreeC. It can be seen that when fine iron oxide particles by the iron oxide sol are dispersed in the catalyst layer, the NOx purification ability is enhanced over a wide temperature range from low temperature to high temperature. Although the comparative example 1 has the iron oxide particle disperse | distributed to the catalyst layer like an Example, its performance is worse than the comparative example 2 which does not contain an iron oxide. In the case of Comparative Example 1, the iron oxide particles are derived from ferric nitrate and the particle size is large, so the oxygen storage capacity and NOx adsorption capacity of the CeZr composite oxide are not increased. It is considered that the iron oxide particles lowered the specific surface area of the CeZr composite oxide particles and deteriorated the performance.
−耐硫黄被毒性、硫黄被毒からの回復性−
上記実施例及び比較例1,2の各触媒について、上記エージング→硫黄被毒処理→還元処理(硫黄被毒からの回復処理)を順に行ない、該エージング後、硫黄被毒後及び還元処理後各々の触媒入口ガス温度350℃でのリーンNOx浄化率を測定した。
-Sulfur resistance and recovery from sulfur poisoning-
About each catalyst of the said Example and Comparative Examples 1 and 2, the said aging-> sulfur poisoning process-> reduction process (recovery process from sulfur poisoning) is performed in order, and after this aging, after sulfur poisoning, and after a reduction process, respectively The lean NOx purification rate at a catalyst inlet gas temperature of 350 ° C. was measured.
硫黄被毒処理は、触媒にN2100%ガスを流通させながら、350℃まで昇温して同温度に保持し、次いで同温度でSO2=100ppm,O2=10%,残N2の硫黄被毒用ガスに切り替えてこれを1時間流通させ(SV=35000/h)、その後N2100%ガスに切り替えて室温まで温度を下げる、というものである。還元処理は、触媒にA/F=14相当のリッチモデル排気ガスを流通させながら(SV=80000/h)、30℃/分で600℃まで昇温させ、その温度に10分間保持した後、N2100%ガスに切り替えて室温まで温度を下げるというものである。 In the sulfur poisoning treatment, while flowing 100% N 2 gas through the catalyst, the temperature was raised to 350 ° C. and maintained at the same temperature, and then at the same temperature, SO 2 = 100 ppm, O 2 = 10%, and the remaining N 2 The gas is switched to sulfur poisoning gas and allowed to flow for 1 hour (SV = 35000 / h), and then switched to N 2 100% gas to lower the temperature to room temperature. In the reduction treatment, the rich model exhaust gas corresponding to A / F = 14 was circulated through the catalyst (SV = 80000 / h), the temperature was raised to 600 ° C. at 30 ° C./min, and maintained at that temperature for 10 minutes. The temperature is lowered to room temperature by switching to N 2 100% gas.
結果を図27に示す。実施例は、硫黄被毒処理によるリーンNOx浄化率の低下度合いが比較例1,2に比べて小さい。これは、酸化鉄ゾルによる微細酸化鉄粒子が硫黄成分SO2を吸着し、NOxトラップ材の被毒を抑制したためと考えられる。そうして、実施例では、還元処理により、リーンNOx浄化率が硫黄被毒前の値まで略完全に回復しており、還元処理を適宜行なうことにより、触媒を長期間にわたって使用することができることがわかる。 The results are shown in FIG. In the embodiment, the degree of decrease in the lean NOx purification rate due to the sulfur poisoning treatment is smaller than those in Comparative Examples 1 and 2. This is considered because the fine iron oxide particles by the iron oxide sol adsorbed the sulfur component SO 2 and suppressed poisoning of the NOx trap material. Thus, in the examples, the reduction treatment has almost completely recovered the lean NOx purification rate to the value before sulfur poisoning, and the catalyst can be used for a long period of time by appropriately performing the reduction treatment. I understand.
1 ハニカム担体のセル壁
2 触媒層
3 Ce含有酸化物粒子
4 バインダ粒子(酸化鉄粒子)
5 触媒金属
6 アルミナ粒子
7 ポア
8 NOxトラップ材
1 Cell wall of honeycomb carrier 2 Catalyst layer 3 Ce-containing oxide particles 4 Binder particles (iron oxide particles)
5 Catalytic metal 6 Alumina particles 7 Pore 8 NOx trap material
Claims (5)
上記触媒層には、酸化鉄粒子が多数分散して含まれ、少なくとも一部の酸化鉄粒子は粒径が300nm以下の微細酸化鉄粒子であり、上記Ce含有酸化物粒子及びNOxトラップ材に当該微細酸化鉄粒子が接触しており、電子顕微鏡観察において、上記微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率が30%以上であることを特徴とする排気ガス浄化用触媒。 For exhaust gas purification in which a Ce-containing oxide particle having oxygen storage / release capability, a NOx trap material other than the Ce-containing oxide particle, and a catalyst layer having Pt and Rh as catalyst metals are formed on a carrier A catalyst,
The catalyst layer includes a large number of dispersed iron oxide particles, at least some of the iron oxide particles are fine iron oxide particles having a particle size of 300 nm or less, and the Ce-containing oxide particles and the NOx trap material An exhaust gas purifying catalyst, wherein the fine iron oxide particles are in contact with each other, and the area ratio of the fine iron oxide particles to the total area of the iron oxide particles is 30% or more in an electron microscope observation.
上記微細酸化鉄粒子は、上記触媒層においてバインダの少なくとも一部を構成していることを特徴とする排気ガス浄化用触媒。 In claim 1,
The exhaust gas purifying catalyst, wherein the fine iron oxide particles constitute at least a part of a binder in the catalyst layer.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることを特徴とする排気ガス浄化用触媒。 In claim 1 or claim 2,
An exhaust gas purifying catalyst, wherein at least a part of the fine iron oxide particles is hematite.
上記微細酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることを特徴とする排気ガス浄化用触媒。 In any one of Claim 1 thru | or 3,
The fine iron oxide particles are made from a sol in which maghemite, goethite, and wustite are dispersed as colloidal particles as a raw material.
自動車の排気ガスのNOxを浄化するリーンNOx触媒として用いられることを特徴とする排気ガス浄化用触媒。 In any one of Claims 1 thru | or 4,
An exhaust gas purification catalyst characterized by being used as a lean NOx catalyst for purifying NOx in automobile exhaust gas.
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2008143511A JP4666007B2 (en) | 2008-05-30 | 2008-05-30 | Exhaust gas purification catalyst |
EP09158900A EP2127729A1 (en) | 2008-05-30 | 2009-04-28 | Exhaust gas purification catalyst |
US12/473,918 US20090298673A1 (en) | 2008-05-30 | 2009-05-28 | Exhaust gas purification catalyst |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2008143511A JP4666007B2 (en) | 2008-05-30 | 2008-05-30 | Exhaust gas purification catalyst |
Publications (2)
Publication Number | Publication Date |
---|---|
JP2009285620A JP2009285620A (en) | 2009-12-10 |
JP4666007B2 true JP4666007B2 (en) | 2011-04-06 |
Family
ID=41455367
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP2008143511A Expired - Fee Related JP4666007B2 (en) | 2008-05-30 | 2008-05-30 | Exhaust gas purification catalyst |
Country Status (1)
Country | Link |
---|---|
JP (1) | JP4666007B2 (en) |
Families Citing this family (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP5181839B2 (en) * | 2008-05-30 | 2013-04-10 | マツダ株式会社 | Exhaust gas purification catalyst |
JP6466629B1 (en) * | 2017-02-28 | 2019-02-06 | 日鉄ケミカル&マテリアル株式会社 | Honeycomb substrate for catalyst support, catalytic converter for exhaust gas purification |
JP7379247B2 (en) * | 2020-03-27 | 2023-11-14 | 日本碍子株式会社 | Porous ceramic structure and method for manufacturing porous ceramic structure |
Citations (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS54117388A (en) * | 1978-03-06 | 1979-09-12 | Kawasaki Steel Co | Preparation of catalyst for removing nitrogen oxide |
JPS62197152A (en) * | 1986-02-25 | 1987-08-31 | Sumitomo Cement Co Ltd | Catalyst related material |
JPH0847640A (en) * | 1994-08-04 | 1996-02-20 | Toyota Central Res & Dev Lab Inc | Catalyst for purification of exhaust gas and purifying method of exhaust gas |
JPH11207190A (en) * | 1998-01-27 | 1999-08-03 | Mazda Motor Corp | Catalyst for purification of exhaust gas and its production |
JP2003126694A (en) * | 2001-10-25 | 2003-05-07 | Toyota Motor Corp | Catalyst for cleaning exhaust gas |
JP2006326554A (en) * | 2005-05-30 | 2006-12-07 | Nissan Motor Co Ltd | Catalyst for purifying exhaust gas, and method for producing it |
JP2007229641A (en) * | 2006-03-01 | 2007-09-13 | Nissan Motor Co Ltd | Catalyst for cleaning exhaust gas and its manufacturing method |
JP2007307485A (en) * | 2006-05-18 | 2007-11-29 | Toyota Central Res & Dev Lab Inc | Nox storage reduction type catalyst |
JP2007534467A (en) * | 2004-02-06 | 2007-11-29 | ハーテーエー・アクチェンゲゼルシャフト・ザ・ハイ・スループット・イクスペリメンテイション・カンパニー | Noble metal catalyst stabilized with iron oxide for removing pollutants from exhaust gas from lean burn engine |
JP2008018322A (en) * | 2006-07-12 | 2008-01-31 | Toyota Motor Corp | Exhaust gas purifying catalyst and its manufacturing method |
-
2008
- 2008-05-30 JP JP2008143511A patent/JP4666007B2/en not_active Expired - Fee Related
Patent Citations (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS54117388A (en) * | 1978-03-06 | 1979-09-12 | Kawasaki Steel Co | Preparation of catalyst for removing nitrogen oxide |
JPS62197152A (en) * | 1986-02-25 | 1987-08-31 | Sumitomo Cement Co Ltd | Catalyst related material |
JPH0847640A (en) * | 1994-08-04 | 1996-02-20 | Toyota Central Res & Dev Lab Inc | Catalyst for purification of exhaust gas and purifying method of exhaust gas |
JPH11207190A (en) * | 1998-01-27 | 1999-08-03 | Mazda Motor Corp | Catalyst for purification of exhaust gas and its production |
JP2003126694A (en) * | 2001-10-25 | 2003-05-07 | Toyota Motor Corp | Catalyst for cleaning exhaust gas |
JP2007534467A (en) * | 2004-02-06 | 2007-11-29 | ハーテーエー・アクチェンゲゼルシャフト・ザ・ハイ・スループット・イクスペリメンテイション・カンパニー | Noble metal catalyst stabilized with iron oxide for removing pollutants from exhaust gas from lean burn engine |
JP2006326554A (en) * | 2005-05-30 | 2006-12-07 | Nissan Motor Co Ltd | Catalyst for purifying exhaust gas, and method for producing it |
JP2007229641A (en) * | 2006-03-01 | 2007-09-13 | Nissan Motor Co Ltd | Catalyst for cleaning exhaust gas and its manufacturing method |
JP2007307485A (en) * | 2006-05-18 | 2007-11-29 | Toyota Central Res & Dev Lab Inc | Nox storage reduction type catalyst |
JP2008018322A (en) * | 2006-07-12 | 2008-01-31 | Toyota Motor Corp | Exhaust gas purifying catalyst and its manufacturing method |
Also Published As
Publication number | Publication date |
---|---|
JP2009285620A (en) | 2009-12-10 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
JP4959129B2 (en) | Exhaust gas purification catalyst | |
EP2644271B1 (en) | Nox storage catalyst and process for the abatement of nox | |
JP3758601B2 (en) | NOx storage reduction catalyst | |
EP2127729A1 (en) | Exhaust gas purification catalyst | |
US7863217B2 (en) | Exhaust gas purifying catalyst and exhaust gas purifying method | |
JP2006334490A (en) | Catalyst for cleaning exhaust gas | |
WO2019088302A1 (en) | Oxygen absorbing and releasing material, catalyst, exhaust gas purifying system, and exhaust gas treatment method | |
WO2018198424A1 (en) | Exhaust gas purification catalyst | |
JP4666006B2 (en) | Exhaust gas purification catalyst | |
JP2007289920A (en) | Exhaust-gas cleaning catalyst, its regeneration method, exhaust-gas cleaning apparatus and exhaust-gas cleaning method using it | |
WO2008007628A1 (en) | Catalyst carrier particle, method for producing the same, and exhaust gas purifying catalyst | |
JP4853495B2 (en) | Exhaust gas purification catalyst | |
JP4656188B2 (en) | Exhaust gas purification catalyst | |
JP3704701B2 (en) | Exhaust gas purification catalyst | |
JP4666007B2 (en) | Exhaust gas purification catalyst | |
KR20100037164A (en) | Exhaust gas purifying catalyst | |
JP2007289921A (en) | Exhaust-gas cleaning catalyst and its regeneration method | |
JP2009287528A (en) | Particulate filter with catalyst | |
JP3766568B2 (en) | Exhaust gas purification catalyst and exhaust gas purification method | |
JP5181839B2 (en) | Exhaust gas purification catalyst | |
JP2003020227A (en) | Fine mixed oxide powder, production method thereor and catalyst | |
JP2010051886A (en) | Catalyst for cleaning exhaust gas | |
JP7428681B2 (en) | Exhaust gas purification catalyst | |
JP4656361B2 (en) | Diesel exhaust gas purification device and exhaust gas purification method | |
JP2013072334A (en) | Exhaust gas purifying device and exhaust gas purifying catalyst unit |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20100329 |
|
A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20100708 |
|
A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20100720 |
|
A521 | Request for written amendment filed |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20100830 |
|
TRDD | Decision of grant or rejection written | ||
A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20101214 |
|
A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20101227 |
|
FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20140121 Year of fee payment: 3 |
|
R150 | Certificate of patent or registration of utility model |
Ref document number: 4666007 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
LAPS | Cancellation because of no payment of annual fees |